|Abstract or Summary
- The performances of newly-established gravel incubation systems designed to use unfiltered water for production of unfed salmon fry were evaluated at Netarts Bay, Oregon, and at Little Port Walter, Alaska.
Research was divided into two phases. The first consisted of laboratory studies to develop fry quality testing procedures and to concurrently investigate effects of substrate, stocking density, water velocity, exposure to light, and incubator design on fry quality. The second consisted of field comparisons of gravel incubator fry to parent stock wild fry at the two sites. Fry quality criteria included egg and alevin mortality, frequency of physical abnormalities, migration pattern and timing, post-emergence growth, size and stage of development, and performance in stress tests; size was the primary criterion. Chum salmon incubated without substrate support and exposed periodically to light experienced intense photonegative reaction leading to yolk-sac malformation, high mortality, and loss of fry size; provision of a shallow gravel substrate negated these adverse effects. By comparison, chinook salmon treated similarly experienced milder photonegative reaction arid insignificant mortalities and yolk-sac malformation; fry size and post-emergence growth appeared to be unaffected by substrate rugosity. Apparent water velocities of 50 to 100 cm/hr and stocking densities of 1.29 to 2.58 pink salmon eggs/cm² produced equivalent fry size without accelerated developmental rates. Increasing velocity to 300 cm/hr or density to 5.16 pink salmon eggs/cm² accelerated developmental rates without affecting fry size. The influence was more significant for velocity (p<O. 025) than for density (p<O. 10). Incubator design or substrate rugosity and depth had little influence on relative fry size of chum salmon given favorable conditions of low stocking density and darkness; gravel incubator fry, however, performed better in stress tests than fry incubated on a smooth substrate. Deep and shallow matrix gravel incubator designs at Little Port Walter and two types of shallow matrix gravel incubator designs at Netarts Bay produced fry of at least equivalent size to wild fry; the deep gravel incubator tested at Little Port Walter was stocked at 0.23 eggs/cm³, which is up to nine times higher than stocking densities used in similar systems elsewhere. At Little Port Walter, hatchery fry migrated at a stage of development similar to wild fry, but at Netarts Bay, hatchery fry migrated mostly at less mature
developmental stages than wild fry. Although no difference in size was detected between fry incubated in shallow matrix or deep matrix gravel incubators in laboratory or field studies, judgments on the preferred system must await evaluation at the adult stage.